Cathode active material for lithium secondary battery and lithium secondary battery including the same

ABSTRACT

The cathode active material for a lithium secondary battery according to embodiments of the present invention includes a lithium-transition metal composite oxide particle including a plurality of primary particles, and the lithium-transition metal composite oxide particle includes a lithium-sulfur-containing portion formed between the primary particles. Thereby, it is possible to improve life-span properties and capacity properties by preventing the layer structure deformation of the primary particles and removing residual lithium.

CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

This application claims priority to Korean Patent Applications No.10-2021-0052405 filed on Apr. 22, 2021 in the Korean IntellectualProperty Office (KIPO), the entire disclosure of which is incorporatedby reference herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a cathode active material for a lithiumsecondary battery and a method of manufacturing the same, and moreparticularly, to a lithium metal oxide-based cathode active material fora lithium secondary battery and a method of manufacturing the same.

2. Description of the Related Art

A secondary battery is a battery which can be repeatedly charged anddischarged. With rapid progress of information and communication, anddisplay industries, the secondary battery has been widely applied tovarious portable telecommunication electronic devices such as acamcorder, a mobile phone, a laptop computer as a power source thereof.Recently, a battery pack including the secondary battery has also beendeveloped and applied to an eco-friendly automobile such as a hybridvehicle as a power source thereof.

Examples of the secondary battery may include a lithium secondarybattery, a nickel-cadmium battery, a nickel-hydrogen battery and thelike. Among them, the lithium secondary battery has a high operatingvoltage and a high energy density per unit weight, and is advantageousin terms of a charging speed and light weight, such that developmentthereof has been proceeded in this regard.

The lithium secondary battery may include: an electrode assemblyincluding a cathode, an anode, and a separation membrane (separator);and an electrolyte in which the electrode assembly is impregnated. Inaddition, the lithium secondary battery may further include, forexample, a pouch-shaped outer case in which the electrode assembly andthe electrolyte are housed.

As an active material for a cathode of a lithium secondary battery, alithium-transition metal composite oxide may be used. Examples of thelithium-transition metal composite oxide may include a nickel-basedlithium metal oxide.

A lithium secondary battery having longer life-span, high capacity, andoperational stability is required as the application range thereof isexpanded. In the lithium-transition metal composite oxide used as theactive material for a cathode, when non-uniformity in the chemicalstructure is caused due to precipitation of lithium, etc., it may bedifficult to implement a lithium secondary battery having desiredcapacity and life-span. In addition, when a deformation or a damage ofthe lithium-transition metal composite oxide structure is caused duringrepeated charging and discharging, life-span stability and capacitymaintenance properties may be reduced.

For example, Korean Patent Registration Publication No. 10-0821523discloses a method of removing lithium salt impurities by washing alithium-transition metal composite oxide with water, but there is alimitation in sufficient removal of the impurities, and a damage to thesurface of particles may be caused in a water washing process.

PRIOR ART DOCUMENT Patent Document

(Patent Document) Korean Patent Registration Publication No. 10-0821523

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a cathode activematerial for a lithium secondary battery having improved operationalstability and electrochemical properties, and a method of manufacturingthe same.

Another object of the present invention to provide a lithium secondarybattery including the cathode active material having improvedoperational stability and electrochemical properties.

To achieve the above objects, according to an aspect of the presentinvention, there is provided a cathode active material for a lithiumsecondary battery including: a lithium-transition metal composite oxideparticle including a plurality of primary particles, wherein thelithium-transition metal composite oxide particle comprises alithium-sulfur-containing portion formed between the primary particles.

In some embodiments, the lithium-sulfur-containing portion may have amonoclinic crystal structure.

In some embodiments, a sulfur content in the lithium-transition metalcomposite oxide particle measured through a carbon-sulfur (CS) analyzermay be 2,000 to 7,000 ppm based on a total weight of thelithium-transition metal composite oxide particle.

In some embodiments, an average sulfur signal value of thelithium-sulfur-containing portion measured through energy dispersivespectroscopy (EDS) may be greater than the average sulfur signal valuein the primary particles measured through the EDS.

In some embodiments, the average sulfur signal value of thelithium-sulfur-containing portion measured through the EDS may be 1.2 to3.8 times greater than the average sulfur signal value in the primaryparticles measured through the EDS.

In some embodiments, the lithium-sulfur-containing portion may bederived from a sulfonyl-based compound represented by Structural Formula1 below:

(In Structural Formula 1, n is 0≤n<3, R₁ and R₂ are O⁻, NH₂, NH₃ ⁺, OH,or a hydrocarbon group having 1 to 3 carbon atoms that can besubstituted with a substituent, and the substituent may include ahalogen, cyano group, hydroxyl group, phosphoric acid group, carboxylgroup or a salt thereof).

In some embodiments, the hydrocarbon group included in R₁ and R₂ inStructural Formula 1 may be substituted with or connected to at leastone selected from the group consisting of a carbon-carbon double bond,—O—, —S—, —CO—, —OCO—, —SO—, —CO—O—, —OCO—O—, —SO—CO—, —S—CO—O—,—CO—NH—, —NH—CO—O—, —NR′—,

—S—S— and —SO₂—, and R′ may be a hydrogen atom or an alkyl group having1 to 3 carbon atoms.

In some embodiments, the sulfonyl-based compound may include at leastone of compounds of Formulae 1 to 3 below:

In some embodiments, the primary particles may have a hexagonalclose-packed structure.

In some embodiments, a content of lithium carbonate (Li₂CO₃) remainingon the surface of the lithium-transition metal composite oxide particlemay be 2,500 ppm or less based on the total weight of thelithium-transition metal composite oxide particle, and a content oflithium hydroxide (LiOH) remaining on the surface of thelithium-transition metal composite oxide particle may be 2,000 ppm orless based on the total weight of the lithium-transition metal compositeoxide particle.

According to another aspect of the present invention, there is provideda method of manufacturing a cathode active material for a lithiumsecondary battery including: preparing a preliminary lithium-transitionmetal composite oxide particle; mixing the preliminarylithium-transition metal composite oxide particle with a sulfonyl-basedcompound aqueous solution including the sulfonyl-based compoundaccording to the above-described embodiment; and performing a heattreatment on the mixed preliminary lithium-transition metal compositeoxide particle and the sulfonyl-based compound aqueous solution, toprepare a lithium-transition metal composite oxide particle comprising aplurality of primary particles and a lithium-sulfur-containing portionformed between the primary particles.

In some embodiments, the sulfonyl-based compound aqueous solution may beformed by inputting the sulfonyl-based compound into a solvent, and aweight of the solvent may be 2 to 20% by weight based on the totalweight of the preliminary lithium-transition metal composite oxideparticle.

In some embodiments, an amount of the sulfonyl-based compound input intothe solvent may be 0.5 to 2.5% by weight based on the total weight ofthe preliminary lithium-transition metal composite oxide particles.

In some embodiments, the heat treatment may be performed at 250 to 450°C. under an oxygen atmosphere.

In some embodiments, the preliminary lithium-transition metal compositeoxide particles may be mixed with the sulfonyl-based compound aqueoussolution without water washing treatment.

According to another aspect of the present invention, there is provideda lithium secondary battery including: a cathode which comprises acathode active material layer comprising the cathode active material fora lithium secondary battery according to the above-describedembodiments; and an anode disposed to face the cathode.

The cathode active material according to embodiments of the presentinvention may include lithium-transition metal composite oxide particlesincluding the plurality of primary particles, and the lithium-transitionmetal composite oxide particles may include thelithium-sulfur-containing portion formed between the primary particles.In this case, residual lithium located on the surface of thelithium-transition metal composite oxide reacts with the sulfonyl-basedcompound to be converted into the lithium-sulfur-containing portion,such that initial capacity and battery efficiency properties may beimproved.

In some embodiments, it is possible to form thelithium-sulfur-containing portion having a monoclinic crystal structurebetween the primary particles in the lithium-transition metal compositeoxide. In this case, a specific surface area of the lithium-transitionmetal composite oxide may be reduced, and the surface of the primaryparticles may be protected by the lithium-sulfur-containing portion,thereby improving life-span properties and driving stability of thesecondary battery.

The lithium-sulfur-containing portion having the monoclinic crystalstructure diffuses lithium through a paddle-wheel mechanism, such thatthe battery may have excellent ion conductivity and improved batteryproperties by reducing a resistance in the lithium-transition metalcomposite oxide particles.

In the method of manufacturing a cathode active material according toembodiments of the present invention, a sulfonyl-based compound aqueoussolution may be prepared by inputting a predetermined amount of asulfonyl-based compound into a solvent in an amount of 2 to 20% byweight (‘wt. %’) based on the total weight of the preliminarylithium-transition metal composite oxide, and mixing the same withoutincluding a water washing process. In this case, it is possible toprevent the primary particles of the lithium-transition metal compositeoxide particles from being deformed from the hexagonal close-packedstructure to the face-centered cubic structure during water washingtreatment. Thereby, it is possible to prevent the initial capacity andlife-span properties of the secondary battery from being reduced. Inaddition, residual lithium located on the surface portion of thelithium-transition metal composite oxide particles is removed, such thata deterioration in the life-span properties due to gas generation may beprevented, and battery resistance may be reduced to improve initialcapacity.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a process flow chart illustrating a method of manufacturing acathode active material according to exemplary embodiments;

FIGS. 2 and 3 are a schematic plan view and a cross-sectional view of alithium secondary battery according to exemplary embodiments,respectively;

FIG. 4(a) is an image and FIG. 4(b) is graphs illustrating energydispersive spectroscopy (TEM-EDS) analysis results for analyzingchemical properties of the lithium-transition metal composite oxideparticles according to Example 1; and

FIG. 5 is a TEM-SAED analysis image for evaluating crystallographicproperties of a lithium-sulfur compound of the lithium-transition metalcomposite oxide particles according to Example 1.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide a cathode active materialincluding lithium-transition metal composite oxide particles and alithium secondary battery including the same.

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.However, these embodiments are merely an example, and the presentinvention is not limited to the specific embodiments described as theexample.

In exemplary embodiments, the cathode active material may include alithium-transition metal composite oxide particle including a pluralityof primary particles, and the lithium-transition metal composite oxideparticle may include a lithium-sulfur (Li—S) containing portion formedbetween the primary particles.

In some embodiments, the primary particles may have a single crystal orpolycrystalline structure in crystallography.

For example, the primary particles may include nickel (Ni), and mayfurther include at least one of cobalt (Co) and manganese (Mn).

For example, the primary particles may have a composition represented byFormula 1 below:

Li_(a)Ni_(x)M_(1−x)O_(2+y)   [Formula 1]

In Formula 1, a, x and y may be in a range of 0.9≤a≤1.2, x≥0.5, and−0.1≤y≤0.1. M may represent at least one element selected from Na, Mg,Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al,Ga, C, Si, Sn, Ba or Zr.

In some preferred embodiments, a molar ratio or concentration x of Ni inFormula 1 may be 0.8 or more, and preferably, greater than 0.8.

For example, when employing a composition of high-nickel (high-Ni)contents in which x is 0.8 or more, calcination of thelithium-transition metal composite oxide particles may be performed at arelatively low temperature. In this case, an amount of residual lithiumgenerated on the surface of the lithium-transition metal composite oxideparticles may be increased. Accordingly, a water washing process or anon-water washing process (e.g., an initial wetting method) for removingthe same may be performed. Therefore, when x is 0.8 or more, forexample, the above process for removing the residual lithium may besubstantially significant.

Ni may be provided as a transition metal associated with the output andcapacity of the lithium secondary battery. Therefore, as describedabove, by employing the composition of high-nickel (high-Ni) contents inthe lithium-transition metal composite oxide particles, it is possibleto provide a high-power cathode and a high-power lithium secondarybattery.

In this regard, as the content of Ni is increased, the long-term storagestability and life-span stability of the cathode or the secondarybattery may be relatively deteriorated. However, according to exemplaryembodiments, by including Co, the life-span stability and capacityretention properties may be improved through Mn while maintainingelectrical conductivity.

In some embodiments, the primary particles of the lithium-transitionmetal composite oxide particle may have a hexagonal close-packedstructure. Accordingly, a large amount of lithium and transition metalelements may be included in a stable structure having a layered formeven in a small space, such that the capacity properties and life-spanproperties of the secondary battery may be improved.

In some embodiments, the lithium-sulfur-containing portion may have amonoclinic structure. For example, lithium hydroxide (LiOH) or lithiumcarbonate (Li₂CO₃) remaining on the surface of lithium-transition metalcomposite oxide particle may react with a sulfonyl-based compound to bedescribed below, and then subjected to heat treatment at a predeterminedtemperature, thus to obtain a lithium-sulfur-containing portion having amonoclinic structure. In this case, the residual lithium may beconverted into a structurally stable lithium-sulfur-containing compoundto allow it to exist around the primary particles. Accordingly, initialcapacity and battery efficiency properties may be improved, and adeterioration in life-span properties caused by residual lithium may beprevented.

For example, the crystal structure of the lithium-sulfur-containingportion may be confirmed through transmission electronmicroscope-selected area electron diffraction (TEM-SAED) analysis.

For example, the lithium-sulfur-containing portion may include at leastone of lithium sulfate (Li₂SO₄), lithium sulfate monohydrate(Li₂SO₄.H₂O), lithium ammonium sulfate (Li(NH₄)SO₄), lithiumhydroxylammonium sulfate (Li(NH₃) (OH)SO₄), lithium fluorosulfate(LiSO₃F), lithium hydrogen sulfate (LiHSO₄), and lithium sulfide (Li₂S).

In exemplary embodiments, the lithium-sulfur-containing portion may bederived from a sulfonyl-based compound represented by Structural Formula1 below.

In Structural Formula 1, n may be 0≤n<3, R₁ and R₂ may be O⁻, NH₂, NH₃⁺, OH, or a hydrocarbon group having 1 to 3 carbon atoms that can besubstituted with a substituent, and the substituent may include ahalogen, cyano group, hydroxyl group, phosphoric acid group, carboxylgroup or a salt thereof.

In some embodiments, the hydrocarbon group included in R₁ and R₂ inStructural Formula 1 may be substituted with or connected to at leastone selected from the group consisting of a carbon-carbon double bond,—O—, —S—, —CO—, —OCO—, —SO—, —CO—O—, —OCO—O—, —S—CO—, —S—CO—O—, —CO—NH—,—NH—CO—O—, —NR′—,

—S—S— and —SO₂—, and R′ may be a hydrogen atom or an alkyl group having1 to 3 carbon atoms.

In some embodiments, the above-described sulfonyl-based compound mayinclude at least one of the compounds represented by Formulae 1 to 3below.

For example, the sulfonyl-based compound represented by StructuralFormula 1 described above may be input in a form of a sulfonyl-basedcompound aqueous solution to be described below. In this case, thesulfonyl-based compound may react with lithium remaining on the surfaceof the lithium-transition metal composite oxide particles to form thelithium-sulfur-containing portion. Thereby, residual lithium may beremoved to improve the capacity properties and life-span properties ofthe secondary battery.

In some embodiments, a sulfur content included in the lithium-transitionmetal composite oxide particle may be 2,000 to 7,000 ppm based on atotal weight of the lithium-transition metal composite oxide particles.In this case, while sufficient sulfonyl-based compound reacts with theresidual lithium to improve battery life-span properties, it is possibleto prevent a deterioration in battery output properties due to excessivesulfur concentration.

In some embodiments, an average sulfur signal value in thelithium-sulfur-containing portions measured through energy dispersivespectroscopy (EDS) may be greater than the average sulfur signal valuein the primary particles measured through the EDS. In this case, thelithium-transition metal composite oxide particles may form aconcentration gradient across the primary particles and thelithium-sulfur-containing portion.

In some embodiments, the average sulfur signal value of thelithium-sulfur-containing portion measured through EDS may be 1.2 to 3.8times greater than the average sulfur signal value in the primaryparticles measured through EDS. In this case, thelithium-sulfur-containing portions may be sufficiently formed in theregion between the primary particles to prevent excessive sulfur frombeing remained due to excessive sulfur input, while protecting thesurface of the primary particles. Accordingly, it is possible to preventdeterioration in the initial capacity and capacity efficiency of thebattery while improving the life-span properties of the battery.

In addition, for example, the lithium-sulfur-containing portions havinga monoclinic crystal structure may be sufficiently formed between theprimary particles included in the lithium-transition metal compositeoxide particles. In this case, the surface of the primary particles maybe protected by the lithium-sulfur-containing portions, thereby reducingan area where the primary particles are exposed to an electrolyte.Accordingly, the life-span properties of the secondary battery may beimproved. In addition, as residual lithium on the surface of thelithium-transition metal composite oxide particles has been sufficientlyremoved, the electrochemical properties of the secondary battery may beimproved in this state.

In some embodiments, a content of lithium precursor remaining on thesurface of the lithium-transition metal composite oxide particles may becontrolled.

For example, the content of lithium carbonate (Li₂CO₃) remaining on thesurface of the lithium-transition metal composite oxide particle may be2,500 ppm or less, and the content of lithium hydroxide (LiOH) remainingon the surface of the lithium-transition metal composite oxide particlemay be 2,500 ppm or less.

When the contents of lithium carbonate and lithium hydroxide satisfy theabove ranges, a resistance may be decreased during lithium ion movement,such that the initial capacity properties and output properties of thelithium secondary battery may be improved, and life-span propertiesduring repeated charging and discharging may be enhanced.

In exemplary embodiments, the lithium-sulfur-containing portion may beformed between the primary particles.

For example, the aqueous solution of the sulfonyl-based compound to bedescribed below may permeate between the primary particles by acapillary force. In this case, the sulfonyl-based compound may reactwith residual lithium between the primary particles, and thelithium-sulfur-containing portion may be formed between the primaryparticles by subsequent heat treatment. Accordingly, thelithium-sulfur-containing portion is distributed not only on the surfaceof the secondary particles as a whole but also in a region between theprimary particles, such that even the region between the primaryparticles may be sufficiently protected when impregnated with theelectrolyte.

In addition, for example, residual lithium that was present between theprimary particles may be converted into a lithium-sulfur compound havinga monoclinic crystal structure. In this case, since the lithium-sulfurcompound moves lithium by a paddle-wheel mechanism, excellent lithiumion conductivity may be implemented. Accordingly, the battery resistancemay be reduced and the capacity and output properties of the battery maybe improved.

The paddle-wheel mechanism may refer to a phenomenon in which, forexample, elements including oxygen rotate about sulfur ions constitutinganions and move lithium ions to reduce activation energy required forlithium ion movement.

FIG. 1 is a process flow chart illustrating a method of manufacturing acathode active material according to exemplary embodiments.

Hereinafter, description of the method of manufacturing the cathodeactive material for a lithium secondary battery according to exemplaryembodiments described above will be provided with reference to FIG. 1.

Referring to FIG. 1, a preliminary lithium-transition metal compositeoxide particle may be prepared (e.g., step S10).

For example, the preliminary lithium-transition metal composite oxideparticle may be prepared by reacting a transition metal precursor with alithium precursor. The transition metal precursor (e.g., Ni—Co—Mnprecursor) may be prepared through a co-precipitation reaction.

For example, the transition metal precursor may be prepared through aco-precipitation reaction of metal salts. The metal salts may includenickel salts, manganese salts and cobalt salts.

Examples of the nickel salt may include nickel sulfate, nickelhydroxide, nickel nitrate, nickel acetate, and a hydrate thereof, etc.Examples of the manganese salt may include manganese sulfate, manganeseacetate, and a hydrate thereof, etc. Examples of the cobalt salt mayinclude cobalt sulfate, cobalt nitrate, cobalt carbonate, and a hydratethereof, etc.

The metal salts may be mixed with a precipitant and/or a chelating agentin a ratio satisfying the content of each metal or the concentrationratios described with reference to Formula 1 to prepare an aqueoussolution. The aqueous solution may be co-precipitated in a reactor toprepare the transition metal precursor.

The precipitant may include an alkaline compound such as sodiumhydroxide (NaOH), sodium carbonate (Na₂CO₃) and the like. The chelatingagent may include, for example, ammonia water (e.g., NH₃H₂O), ammoniumcarbonate (e.g., NH₃HCO₃) and the like.

The temperature of the co-precipitation reaction may be controlled, forexample, in a range of about 40° C. to 60° C. The reaction time may becontrolled in a range of about 24 to 72 hours.

The lithium precursor compound may include, for example, lithiumcarbonate, lithium nitrate, lithium acetate, lithium oxide, lithiumhydroxide and the like. These compounds may be used alone or incombination of two or more thereof.

In exemplary embodiments, the sulfonyl-based compound aqueous solutionincluding the above-described sulfonyl-based compound may be input intothe prepared preliminary lithium-transition metal composite oxideparticle and mixed (e.g., step S20).

For example, the sulfonyl-based compound may be a compound representedby Structural Formula 1 described above. Preferably, the sulfonyl-basedcompound may include at least one of the compounds of Formulae 1 to 3described above.

In some embodiments, the sulfonyl-based compound aqueous solution may beformed by inputting the above-described sulfonyl-based compound into asolvent. For example, the solvent may be de-ionized water (DIW).

In exemplary embodiments, the preliminary lithium-transition metalcomposite oxide particle and the sulfonyl-based compound aqueoussolution may be mixed. In this case, the sulfonyl-based compoundcontained in the sulfonyl-based compound aqueous solution may beconverted into a lithium-sulfur-containing portion by reacting withresidual lithium present on the surface of the preliminarylithium-transition metal composite oxide particle. Accordingly, thelithium-transition metal composite oxide particle including the primaryparticles and the lithium-sulfur-containing portion may be obtained.

For example, since ammonium ion (NH4+) contained in the sulfonyl-basedcompound is an ion made of only non-metal elements, it may be vaporizedduring a heat treatment process to be described below. In this case, thelithium-sulfur-containing portion may be lithium sulfate (Li₂SO₄).Accordingly, only lithium ions remain as cations, such that the lithiumions may smoothly move when charging and discharging the battery.

For example, impurities present on the surface of the preliminarylithium-transition metal composite oxide particle may be removed throughthe mixing process. For example, in order to improve a yield of lithiummetal oxide particles or stabilize a synthesis process, the lithiumprecursor (lithium salt) may be used in an excess amount. In this case,a lithium precursor including lithium hydroxide (LiOH) and lithiumcarbonate (Li₂CO₃) may remain on the surface of the preliminarylithium-transition metal composite oxide particle.

In addition, for example, as the lithium-transition metal compositeoxide particle contain the composition of higher-Ni contents,calcination may be performed at a lower temperature when manufacturingthe cathode. In this case, a content of residual lithium on the surfaceof the lithium-transition metal composite oxide particle may beincreased.

When the residual lithium is removed by washing with water (waterwashing treatment) in substantially the same amount as the cathodeactive material, the residual lithium may be removed, but oxidation ofthe surface of the preliminary lithium-transition metal composite oxideparticles and side reactions with water may be caused, thereby resultingin a damage or collapse of the layered structure of the primaryparticles. In addition, as the layered structure is deformed into theface centered cubic structure, spinel structure and/or rock saltstructure rather than the hexagonal close-packed structure by water, thelithium-nickel-based oxide may be hydrolyzed to form nickel impuritiessuch as NiO or Ni(OH)₂. In this case, since the modified structures areirreversible structures, the movement of lithium may be hindered duringcharging and discharging. Accordingly, the initial capacity and capacityretention rate of the secondary battery may be decreased.

However, according to exemplary embodiments of the present application,since the mixing process (e.g., initial wetting method) is performedusing the sulfonyl-based compound aqueous solution without water washingtreatment, passivation due to the potassium-containing compound may beimplemented on the surface of the lithium-transition metal compositeoxide particles while the mixing process is performed. For example, thelithium-sulfur-containing portion having a monoclinic crystal structurein which lithium and sulfur are bonded between primary particles havinga hexagonal close-packed structure may be formed.

The term “initial wetting method” as used herein may refer to, forexample, a method of inputting 20 wt. % or less of water or thesulfonyl-based compound aqueous solution by, for instance, a spraymethod, based on the total weight of the lithium-transition metalcomposite oxide particles without performing water washing treatment ofinputting water in an amount substantially the same as or similar to thetotal weight of the lithium-transition metal composite oxide particlesand stirring.

In addition, since water washing treatment is not performed, forexample, the lithium-transition metal composite oxide particle may notinclude the primary particles having the face centered cubic structure.Therefore, the residual lithium may be effectively removed whilepreventing oxidation and damage to the layered structure due to water onthe particle surface.

For example, when directly mixing (e.g., dry coating) the sulfonyl-basedcompound powder with the lithium-transition metal composite oxideparticle instead of the sulfonyl-based compound aqueous solution, sincethe sulfonyl-based compound powder does not have a capillary force, itcannot permeate between the primary particles, and most of thesulfonyl-based compound powder may react with the residual lithium onthe surface of the secondary particles in which the primary particlesare aggregated. In this case, most of the lithium-sulfur-containingportion may be formed in the form of existing on the surface of thesecondary particles. Accordingly, the average sulfur signal value in thelithium-sulfur-containing portion may be reduced compared to the averagesulfur signal value in the primary particles, which will be describedbelow.

In addition, when performing the dry coating, residual lithium presentbetween the primary particles may not be sufficiently removed.Accordingly, the residual lithium may act as a resistor to reduce thecapacity and output properties of the battery.

According to exemplary embodiments of the present application, theinitial wetting method may be performed using the sulfonyl-basedcompound aqueous solution as described above. In this case, thesulfonyl-based compound aqueous solution may permeate between theprimary particles by the capillary force, and react with residuallithium between the primary particles to form thelithium-sulfur-containing portion between the primary particles.

For example, since the lithium-sulfur-containing portion has themonoclinic crystal structure, ion conductivity is relatively excellent,thereby suppressing an increase in the battery resistance. Accordingly,it is possible to prevent a reduction in the capacity properties whileimproving the life-span properties of the battery.

In some embodiments, an amount of the solvent in the sulfonyl-basedcompound aqueous solution mixed with the preliminary lithium-transitionmetal composite oxide particle may be 2 to 20 wt. % based on the totalweight of the preliminary lithium-transition metal composite oxideparticle. In this case, while the lithium-sulfur-containing portion isalso formed to have appropriate lithium/sulfur contents at a positionwhere the residual lithium was present on the surface of the preliminarylithium-transition metal composite oxide particle, substantially as inthe case of water washing treatment, it is possible to prevent a damageor collapse of the layered structure of the primary particles from beingcaused.

In some embodiments, the amount of the sulfonyl-based compound inputinto the solvent may be 0.5 to 2.5 wt. % based on the total weight ofthe preliminary lithium-transition metal composite oxide particle. Inthis case, while a sufficient amount of the sulfonyl-based compoundreacts with residual lithium to form a lithium-sulfur-containingportion, it is possible to prevent excessively high sulfur content inthe cathode active material. Accordingly, it is possible to maintain theoutput properties while improving the life-span properties of thebattery.

After the mixing process, a cathode active material including theprimary particles and the lithium-sulfur-containing portion may beobtained through a heat treatment (calcination) process (e.g., stepS30).

For example, the preliminary lithium-transition metal composite oxideparticle and the lithium-sulfur-containing portion on which the mixingprocess has been performed may be subjected to heat treatment using acalcination furnace. Accordingly, it is possible to obtainlithium-transition metal composite oxide particles in which thelithium-sulfur-containing portion is fixed between the primaryparticles.

For example, the heat treatment may be performed at 250 to 450° C. underan oxygen atmosphere. In this case, the residual lithium on the surfaceof the preliminary lithium-transition metal composite oxide particle andthe sulfonyl-based compound in the sulfonyl-based compound aqueoussolution may be sufficiently bonded to form thelithium-sulfur-containing portion.

FIGS. 2 and 3 are a schematic plan view and a cross-sectional view of alithium secondary battery according to exemplary embodiments,respectively.

Hereinafter, description of a lithium secondary battery including acathode including the cathode active material for a lithium secondarybattery described above will be provided with reference to FIGS. 2 and3.

Referring to FIGS. 2 and 3, the lithium secondary battery may include acathode 100, an anode 130, and a separation membrane 140 including thecathode active material including the lithium-sulfur-containing portion.

The cathode 100 may include a cathode active material layer 110 formedby applying the above-described cathode active material including thelithium-transition metal oxide particles to a cathode current collector105.

For example, a slurry may be prepared by mixing and stirring thepreliminary lithium-transition metal oxide particles mixed with thesulfonyl-based compound aqueous solution with a binder, a conductivematerial and/or a dispersant in a solvent. The cathode current collector105 may be coated with the slurry, followed by compressing and drying toprepare the cathode.

The cathode current collector 105 may include, for example, stainlesssteel, nickel, aluminum, titanium, copper, or an alloy thereof, andpreferably includes aluminum or an aluminum alloy.

The binder may be selected from, for example, an organic binder such asvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP),polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, etc., or an aqueous binder such as styrene-butadienerubber (SBR), and may be used together with a thickener such ascarboxymethyl cellulose (CMC).

For example, a PVDF-based binder may be used as the binder for formingthe cathode. In this case, an amount of the binder for forming thecathode active material layer 110 may be reduced and an amount of thecathode active material may be relatively increased, thereby improvingthe output and capacity of the secondary battery.

The conductive material may be included to facilitate electron movementbetween the active material particles. For example, the conductivematerial may include a carbon-based conductive material such asgraphite, carbon black, graphene, or carbon nanotubes and/or ametal-based conductive material such as tin, tin oxide, titanium oxide,or a perovskite material such as LaSrCoO₃, and LaSrMnO₃.

The anode 130 may include an anode current collector 125 and an anodeactive material layer 120 formed by coating the anode current collector125 with an anode active material.

The anode active material useable in the present invention may includeany material known in the related art, so long as it can intercalate anddeintercalate lithium ions, without particular limitation thereof. Forexample, carbon-based materials such as crystalline carbon, amorphouscarbon, carbon composite, carbon fiber, etc.; a lithium alloy; a siliconcompound or tin may be used. Examples of the amorphous carbon mayinclude hard carbon, cokes, mesocarbon microbead (MCMB), mesophasepitch-based carbon fiber (MPCF) or the like. Examples of the crystallinecarbon may include graphite-based carbon such as natural graphite,artificial graphite, graphite cokes, graphite MCMB, graphite MPCF or thelike. Other elements included in the lithium alloy may include, forexample, aluminum, zinc, bismuth, cadmium, antimony, silicone, lead,tin, gallium, indium or the like.

The anode current collector 125 may include stainless steel, nickel,aluminum, titanium, copper, or an alloy thereof, and preferably includesaluminum or an aluminum alloy.

In some embodiments, a slurry may be prepared by mixing the anode activematerial with an anode forming binder, a conductive material and/or adispersant in a solvent. The anode current collector may be coated withthe slurry, followed by compressing and drying to prepare the anode 130.

As the binder and the conductive material, materials which aresubstantially the same as or similar to the above-described materialsmay be used. In some embodiments, the binder for forming the anode mayinclude, for example, an aqueous binder such as styrene-butadiene rubber(SBR) for consistency with the carbon-based active material, and may beused together with a thickener such as carboxymethyl cellulose (CMC).

The separation membrane 140 may be interposed between the cathode 100and the anode 130. The separation membrane 140 may include a porouspolymer film made of a polyolefin polymer such as ethylene homopolymer,propylene homopolymer, ethylene/butene copolymer, ethylene/hexenecopolymer, ethylene/methacrylate copolymer. The separation membrane 140may include a nonwoven fabric made of glass fiber having a high meltingpoint, polyethylene terephthalate fiber or the like.

According to exemplary embodiments, an electrode cell is defined by thecathode 100, the anode 130, and the separation membrane 140, and aplurality of the electrode cells are stacked to form a jelly roll typeelectrode assembly 150, for example. For example, the electrode assembly150 may be formed by winding, lamination, folding, or the like of theseparation membrane 140. The electrode assembly may be housed in anouter case 160 together with the electrolyte, such that a lithiumsecondary battery may be defined. According to exemplary embodiments, anon-aqueous electrolyte may be used as the electrolyte.

The non-aqueous electrolyte includes a lithium salt as an electrolyteand an organic solvent. The lithium salt is represented by, for example,Li⁺X⁻ and may include F⁻, Cl⁻, Br⁻, I⁻, NO₃ ⁻, N(CN)₂ ⁻, BF₄ ⁻, ClO₄ ⁻,PF₆ ⁻, (CF₃)₂PF₄ ⁻, (CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻, (CF₃)₆P⁻,CF₃SO₃ ⁻, CF₃CF₂SO₃ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻, CF₃CF₂(CF₃)₂CO⁻,(CF₃SO₂)₂CH⁻, (SF₅)₃C⁻, (CF₃SO₂)₃C⁻, CF₃(CF₂)₇SO₃ ⁻, CF₃CO₂ ⁻, CH₃CO₂ ⁻,SCN⁻, (CF₃CF₂SO₂)₂N⁻, and the like as an example.

Examples of the organic solvent may use any one of propylene carbonate(PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethylcarbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate,dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane,diethoxyethane, vinylene carbonate, sulforane, γ-butyrolactone,propylene sulfite, and tetrahydrofurane, or a mixture of two or morethereof. These compounds may be used alone or in combination of two ormore thereof.

As shown in FIG. 3, electrode tabs (a cathode tab and an anode tab) mayprotrude from the cathode current collector 105 and the anode currentcollector 125, respectively, which belong to each electrode cell, andmay extend to one side of the outer case 160. The electrode tabs may befused together with the one side of the outer case 160 to form electrodeleads (a cathode lead 107 and an anode lead 127) extending or exposed toan outside of the outer case 160.

The lithium secondary battery may be manufactured, for example, in acylindrical shape using a can, a square shape, a pouch type or a coinshape.

According to exemplary embodiments, a lithium secondary battery havingimproved life-span and long-term stability while suppressing a decreasein capacity and average voltage by improving chemical stability of thecathode active material by doping or coating with the sulfonyl-basedcompound may be implemented.

Hereinafter, experimental examples including specific examples andcomparative examples will be described to more concretely understand thepresent invention. However, those skilled in the art will appreciatethat such examples are provided for illustrative purposes and do notlimit subject matters to be protected as disclosed in appended claims.Therefore, it will be apparent to those skilled in the art variousalterations and modifications of the embodiments are possible within thescope and spirit of the present invention and duly included within therange as defined by the appended claims.

Example 1 Preparation of Preliminary Lithium-Transition Metal CompositeOxide Particles (S10)

NiSO₄, CoSO₄ and MnSO₄ were mixed in a ratio of 0.885:0.090:0.025,respectively, using distilled water from which internal dissolved oxygenis removed by bubbling with N₂ for 24 hours. The solution was input intoa reactor at 50° C., and a co-precipitation reaction was performed for48 hours using NaOH and NH₃H₂O as a precipitant and a chelating agent toobtain Ni_(0.885)Co_(0.09)Mn_(0.025)(OH)₂ as a transition metalprecursor. The obtained precursor was dried at 80° C. for 12 hours, andthen again dried at 110° C. for 12 hours.

Lithium hydroxide and the transition metal precursor were added to a dryhigh-speed mixer in a ratio of 1.01:1, and the mixture was uniformlymixed for 5 minutes. The mixture was put into a calcination furnace, andheated to 730 to 750° C. at a heating rate of 2° C./min, then maintainedat 730 to 750° C. for 10 hours. Oxygen was passed continuously at a flowrate of 10 mL/min during heating and maintenance. After completion ofthe calcination, the mixture was naturally cooled to room temperature,followed by grinding and classification to prepare a preliminarylithium-transition metal composite oxide particleLiNi_(0.885)Co_(0.09)Mn_(0.025)O₂.

Preparation and Mixing of Sulfonyl-Based Compound Aqueous Solution(S20), and Heat Treatment (S30)

Ammonium sulfate (NH₄(SO₄)) powder in an amount of 1.2 wt. % based onthe total weight of the preliminary lithium-transition metal compositeoxide particles was input into de-ionized water (DIW) in an amount of 5wt. % based on the total weight of the preliminary lithium-transitionmetal composite oxide particles, and then the mixture was stirred sothat the ammonium sulfate powder was sufficiently dissolved the inde-ionized water to prepare a sulfonyl compound aqueous solution.

The prepared sulfonyl-based compound aqueous solution was input into theobtained preliminary lithium-transition metal composite oxide particlesand mixed.

The mixture was put into the calcination furnace, heated to atemperature of 400° C. at a heating rate of 2° C./min while supplyingoxygen at a flow rate of 20 mL/min, and maintained at the heatedtemperature for 10 hours. After completion of the calcination, thecalcined product was classified by 325 mesh to obtain a cathode activematerial.

Manufacture of lithium secondary battery

A secondary battery was manufactured using the above-described cathodeactive material. Specifically, the cathode active material, Denka Blackas a conductive material, and PVDF as a binder were mixed in a massratio composition of 93:5:2, respectively, to prepare a cathode slurry.Then, the slurry was applied to an aluminum current collector, followedby drying and pressing the same to prepare a cathode. After the press, atarget electrode density of the cathode was adjusted to 3.0 g/cc.

Lithium metal was used as an anode active material.

The cathode and anode prepared as described above were notched in acircular shape having a diameter of Φ14 and Φ16, respectively, andlaminated, then an electrode cell was prepared by disposing a separationmembrane (polyethylene, thickness: 13 μm) notched to Φ19 between thecathode and the anode. The prepared electrode cell was put into a coincell outer case having a specification of diameter of 20 mm and a heightof 1.6 mm, then an electrolyte was injected and assembled, followed byaging for 12 hours or more so that the electrolyte could be impregnatedinside the electrodes.

The electrolyte used herein was prepared by dissolving 1M LiPF₆ solutionin a mixed solvent of EC/EMC (30/70; volume ratio).

The secondary battery manufactured as described above was subjected toformation charging-discharging (charge condition: CC-CV 0.1 C 4.3 V0.005 C CUT-OFF, discharge condition: CC 0.1 C 3 V CUT-OFF).

Example 2

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatthe ammonium sulfate powder was input into the de-ionized water in anamount of 0.8 wt. % based on the total weight of the preliminarylithium-transition metal composite oxide particle.

Example 3

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatthe ammonium sulfate powder was input into the de-ionized water in anamount of 1.6 wt. % based on the total weight of the preliminarylithium-transition metal composite oxide particle.

Example 4

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatthe ammonium sulfate powder was input into the de-ionized water in anamount of 2.0 wt. % based on the total weight of the preliminarylithium-transition metal composite oxide particle.

Example 5

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatthe ammonium sulfate powder was input into the de-ionized water in anamount of 2.4 wt. % based on the total weight of the preliminarylithium-transition metal composite oxide particle.

Example 6

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatammonium sulfate powder was input into the de-ionized water in an amountof 0.4 wt. % based on the total weight of the preliminarylithium-transition metal composite oxide particle.

Example 7

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatthe ammonium sulfate powder was input into the de-ionized water in anamount of 2.8 wt. % based on the total weight of the preliminarylithium-transition metal composite oxide particle.

Example 8

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatthe temperature was raised to 200° C. in the calcination furnace.

Example 9

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatthe temperature was raised to 500° C. in the calcination furnace.

Example 10

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatthe same amount of ammonium sulfamate (NH₄ (SO₃NH₂)) was input into thede-ionized water instead of the ammonium sulfate.

Example 11

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatthe same amount of sulfamic acid (SO₂NH₂OH) was input into thede-ionized water instead of the ammonium sulfate.

Comparative Example 1

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1 except thati) to iii) as below,

i) without performing the step of mixing the preliminarylithium-transition metal composite oxide particles with thesulfonyl-based compound aqueous solution,

ii) the preliminary lithium-transition metal composite oxide particleswere input into 100 wt. % of de-ionized water based on the total weightof the preliminary lithium-transition metal composite oxide particles,and

iii) the mixture was subjected to water washing treatment by stirringfor 10 minutes, followed by drying at 130 to 170° C. under vacuum for 12hours after filtering.

Comparative Example 2

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatde-ionized water was input in an amount of 5 wt. % based on the totalweight of the preliminary lithium-transition metal composite oxideparticles instead of the sulfonyl-based compound aqueous solution andmixed.

The above-described examples and Comparative Example 2 were performed bythe initial wetting method in which a small amount of solution or waterwas input, not the water washing treatment in which substantially thesame amount of water as the cathode active material was input, and inComparative Example 1, the water washing treatment was performed.

Comparative Example 3

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except that,ammonium sulfate (NH₄(SO₄)) powder was input in an amount of 1.2 wt. %based on the total weight of the preliminary lithium-transition metalcomposite oxide particle and mixed with the preliminarylithium-transition metal composite oxide particle (dry mixing) insteadof the sulfonyl-based compound aqueous solution.

Process types, types and input amounts of the sulfonyl-based compound,and heat treatment temperatures of the above-described examples andcomparative examples are shown in Table 1 below.

TABLE 1 sulfonyl- based Heat Sulfonyl- compound treatment Process basedinput amount temperature Section type compound type (wt. %) (° C.)Example 1 Initial Ammonium 1.2 400 wetting sulfate Example 2 InitialAmmonium 0.8 400 wetting sulfate Example 3 Initial Ammonium 1.6 400wetting sulfate Example 4 Initial Ammonium 2.0 400 wetting sulfateExample 5 Initial Ammonium 2.4 400 wetting sulfate Example 6 InitialAmmonium 0.4 400 wetting sulfate Example 7 Initial Ammonium 2.8 400wetting sulfate Example 8 Initial Ammonium 1.2 200 wetting sulfateExample 9 Initial Ammonium 1.3 500 wetting sulfate Example 10 InitialAmmonium 1.2 400 wetting sulfamate Example 11 Initial Sulfamic acid 1.2400 wetting Comparative Water — — 400 Example 1 washing treatmentComparative Water — — 400 Example 2 washing treatment Comparative Drymixing Ammonium 1.2 400 Example 3 sulfate

Experimental Example (1) TEM-EDS (Transmission ElectronMicroscope-Energy Dispersive Spectroscopy) Image Analysis

The lithium-transition metal composite oxide particles preparedaccording to the above-described examples and comparative examples werecontinuously measured by line scan to obtain nickel and sulfur signalvalues in a primary particle region and the region between the primaryparticles (e.g., lithium-sulfur-containing portion) through STEM-EDS.Thereafter, by averaging the sulfur signal values for each region, anaverage sulfur signal value of the primary particles and thelithium-sulfur-containing portion was calculated.

(2) Measurement of Sulfur (S) Content

To measure a content of sulfur (S) of the lithium-transition metalcomposite oxide particles obtained according to the above-describedexamples and comparative examples, a C/S analyzer (carbon/sulfuranalysis equipment; model name: CS844, manufacturer: LECO) was used, andan amount of sample was selected according to the range of measurementvalues of the standard sample measured when drawing up a calibrationcurve.

Specifically, 0.02 to 0.04 g of lithium-transition metal composite oxideparticles obtained according to the above-described examples andcomparative examples were input into the ceramic crucible, and acombustion improver (LECOCEL II) and IRON chips were mixed in a ratio of1:1 together. Thereafter, O₂ was supplied as a combustion gas at 3 L/minin a high-frequency induction furnace and burned at about 2,600 to2,700° C., and the sulfur oxide-based inorganic compound gas (e.g.,sulfuric acid gas) generated by the combustion was passed through aninfrared detection cell. At this time, a change in infrared absorptioncompared to the blank was measured to quantitatively detect the sulfurcontent in the lithium-transition metal composite oxide particles.

(3) Measurement of Residual Lithium (Li₂CO₃, LiOH) Content

1.5 g of each of the cathode active materials of the examples andcomparative examples was quantified in a 250 mL flask, 100 g ofdeionized water was input then a magnetic bar was put thereto, and themixture was stirred at a speed of 60 rpm for 10 minutes. Thereafter, 100g was sampled after filtering using a flask at reduced pressure. Thesampled solution was put into a container of automatic titrator andautomatically titrated with 0.1N HCl referring to the Wader's method tomeasure Li₂CO₃ and LiOH contents in the solution.

(4) Measurement of Initial Charge/Discharge Capacity and Evaluation ofInitial Capacity Efficiency

After charging (CC-CV 0.1 C 4.3 V 0.005 C CUT-OFF) the lithium secondarybatteries manufactured according to the above-described examples andcomparative examples in a chamber at 25° C., battery capacities (initialcharge capacities) were measured, and after discharging again (CC 0.1 C3.0 V CUT-OFF) the same, the battery capacities (initial dischargecapacities) were measured.

Initial capacity efficiency of each lithium secondary battery wascalculated by dividing the measured initial discharge capacity by themeasured initial charge capacity, then converting it into a percentage(%).

(5) Measurement of Capacity Retention Rate (Life-Time (Cycle)Properties) During Repeated Charging and Discharging

The lithium secondary batteries according to the examples andcomparative examples were repeatedly charged (CC/CV 0.5 C 4.3 V 0.05 CCUT-OFF) and discharged (CC 1.0 C 3.0 V CUT-OFF) 100 times, then thecapacity retention rate was evaluated as a percentage of the dischargecapacity at 100 times divided by the discharge capacity at one time.

(6) Calculation of Sulfur Signal Ratio

In the lithium-transition metal composite oxide particles obtainedaccording to Examples 1 to 9 and Comparative Examples 2 and 3, lithiumand sulfur signals in the primary particle region and thelithium-sulfur-containing portion were measured through SEM-EDS.

Thereafter, an average sulfur signal value was measured by averaging thesulfur signal values for each of the primary particle region and thelithium-sulfur-containing portion, and then the average sulfur signalvalue of the lithium-sulfur-containing portion was divided by theaverage sulfur signal value in the primary particles to calculate asulfur signal ratio.

The evaluation results are shown in Table 2 below.

TABLE 2 Initial Initial Initial Capacity Sulfur Sulfur Li₂CO₃ LiOHcharge discharge capacity retention content signal content contentcapacity capacity efficiency rate Section (ppm) ratio (ppm) (ppm)(mAh/g) (mAh/g) (%) (%) Example 1 3,200 2.0 1,880 1,400 238.8 213.889.5% 87 Example 2 2,400 1.5 2,240 1,690 238.7 213 89.2% 85 Example 34,100 2.5 1,690 1,330 238.8 212.9 89.2% 86 Example 4 5,000 3.1 1,6601,510 238.4 211.8 88.8% 86 Example 5 6,200 3.6 1,520 1,760 238.3 210.288.2% 87 Example 6 1,900 1.1 2,610 2,020 238.5 212.5 89.1% 82 Example 77,100 3.9 1,390 1,660 238.6 209.5 87.8% 86 Example 8 3,000 1.9 2,5201,910 238.8 214.4 89.8% 79 Example 9 3,100 2.0 1,590 1,220 238.6 208.387.3% 87 Example 10 2,700 — 1,660 1,560 238 213.4 89.7% 86 Example 112,800 — 1,080 1,850 238.8 212.5 89.0% 86 Comparative 130 — 1,230 1,390237.1 209 88.1% 62 Example 1 Comparative 1,100 1.0 3,010 2,630 238.3212.1 89.0% 80 Example 2 Comparative 3,000 1.2 3,500 2,500 237.2 207.887.6% 88 Example 3

FIGS. 4(a) and 4(b) are image and graphs, respectively, illustratingenergy dispersive spectroscopy (TEM-EDS) analysis results for analyzingchemical properties of the lithium-transition metal composite oxideparticles according to Example 1. Specifically, FIG. 4(a) is an imageillustrating the primary particles of the lithium-transition metalcomposite oxide particles obtained according to Example 1 and the regionbetween the primary particles, and FIG. 4(b) is graphs illustratingnickel and sulfur signal values of the primary particle region and theregion (e.g., lithium-sulfur-containing portion) between primaryparticles of Example 1.

Referring to FIG. 4, the primary particles and thelithium-sulfur-containing portion may be distinguished through atransition of nickel signal value. As shown in FIG. 4, in the case ofExample 1, it can be seen that the nickel signal in thelithium-sulfur-containing portion is decreased and the sulfur signal isincreased. Accordingly, the primary particles may be high-Ni particles,and the lithium-sulfur-containing portion may be an interface betweenthe primary particles, wherein a sulfur component may be concentrated.

FIG. 5 is a selected area electron diffraction (TEM-SAED) analysis imagefor evaluating crystallographic properties of the lithium-sulfurcompound of the lithium-transition metal composite oxide particlesaccording to Example 1.

Referring to FIG. 5, it can be confirmed that the lithium-sulfurcompound of the lithium-transition metal composite oxide particles ofExample 1 prepared through the initial wetting method has a monocliniccrystal structure.

Specifically, in order to analyze the crystal structure on thecross-sections of the lithium-transition metal composite oxide particlesobtained according to the above-described Example 1, a TEM-SAED analysiswas performed on the lithium-sulfur-containing portion present betweenthe primary particles. The lithium-sulfur-containing portion wasdesignated by a selected area aperture and then entered into adiffraction mode to obtain a diffraction image. A [010] region of themonoclinic crystal structure may be confirmed through the obtaineddiffraction image.

Referring to Table 2, the examples in which the initial wetting methodwas performed by mixing the sulfonyl-based compound aqueous solutionexhibited good initial capacity efficiency and capacity retention ratewhile reducing the lithium content remaining on the surface of thelithium-transition metal composite oxide particles compared to thecomparative examples as a whole.

However, in the case of Example 6 in which the sulfonyl-based compoundwas input in an amount of less than 0.5 wt. %, the residual lithium wasslightly increased due to an insufficient amount of the sulfonyl-basedcompound to react with the residual lithium, and the capacity retentionrate was also reduced, compared to Examples 1 to 5.

In addition, in the case of Example 7 in which the sulfonyl-basedcompound was input exceeding 2.5 wt. %, residual lithium wassufficiently removed, but excess sulfur remained, thereby reducing theinitial capacity and capacity efficiency of the battery.

Further, in the case of Example 8 in which the heat treatmenttemperature was less than 250° C., the capacity efficiency wasexcellent, but reactivity with the residual lithium was relativelydecreased, such that the residual lithium was relatively increased.Furthermore, since an ammonium functional group present in thesulfonyl-based compound does not sufficiently react with lithium or isnot vaporized at a low temperature and remains as an impurity in thelithium-transition metal composite compound particles, batteryproperties including life-span properties were deteriorated.

In addition, in the case of Example 9 in which the heat treatmenttemperature was greater than 450° C., the life-span properties weremaintained, but the capacity efficiency was greatly decreased.Specifically, the lithium-sulfur-containing compound having themonoclinic structure might have improved structural crystallinity andincreased bonding strength with lithium as the heat treatmenttemperature was increased. Accordingly, the lithium ion conductivitythrough the paddle-wheel mechanism was reduced, thereby decreasing thecapacity efficiency.

In the case of Comparative Example 1 using the conventional waterwashing method, the residual lithium was removed to a high level, but asthe layered structure of the primary particles was deformed during thewater washing treatment, the initial capacity, efficiency, life-span andelectrochemical properties were greatly reduced.

In the case of Comparative Example 2 using the initial wetting method,but not using the sulfonyl-based compound, the residual lithium was notsufficiently removed.

In the case of Comparative Example 3, in which dry coating was performedusing powder rather than the sulfonyl-based compound solution, theresidual lithium in the region between the primary particles was notsufficiently reacted, such that the residual lithium was measured to behigh, and thus the resistance was high. Thereby, electrochemicalproperties such as initial capacity and efficiency were reduced.

Further, in Examples 1 to 5, a ratio of the average sulfur signal valuein the region between the primary particles to the average sulfur signalvalue in the primary particles (the sulfur signal ratio) satisfied arange of 1.2 to 3.8.

As an example, in the case of Example 1, the signal ratio of sulfur wasshown as 1.9 times from the region between the primary particles (e.g.,lithium-sulfur-containing portion) to the 40 nm section.

However, Example 6, in which the amount of the sulfonyl-based compoundpowder input was less than 0.5 wt. % based on the preliminarylithium-transition metal composite oxide particles, exhibited a lowsulfur signal ratio of less than 1.2 times, such that it was somewhatdifficult to determine the lithium-sulfur-containing portion inlithium-transition metal composite oxide particles.

In addition, in the case of Example 7, in which the amount of thesulfonyl-based compound powder was greater than 2.5 wt. %

based on the preliminary lithium-transition metal composite oxideparticles, the sulfur signal ratio exceeded 3.8 times.

Further, in the case of Comparative Example 3, in which thesulfonyl-based compound powder was input and dry coating was performed,the sulfur signal ratio in the region between the primary particles was1.2 based on that of the region within the primary particles, which wasmeasured significantly lower than 1.9 of Example 1 in which the initialwetting method was performed by inputting the same amount of thesulfonyl-based compound in the form of an aqueous solution.

DESCRIPTION OF REFERENCE NUMERALS

-   100: Cathode-   105: Cathode current collector-   107: Cathode lead-   110: Cathode active material layer-   120: Anode active material layer-   125: Anode current collector-   127: Anode lead-   130: Anode-   140: Separation membrane-   150: Electrode assembly-   160: Case

What is claimed is:
 1. A method of manufacturing a cathode activematerial for a lithium secondary battery comprising: preparing apreliminary lithium-transition metal composite oxide particle; mixingthe preliminary lithium-transition metal composite oxide particle with asulfonyl-based compound aqueous solution including the sulfonyl-basedcompound represented by Structural Formula 1 below; and performing adrying and a heat treatment on the mixed preliminary lithium-transitionmetal composite oxide particle and the sulfonyl-based compound aqueoussolution, to prepare a lithium-transition metal composite oxide particlecomprising a plurality of primary particles and alithium-sulfur-containing portion formed between the primary particles:

(In Structural Formula 1, n is 0≤n<3, R₁ and R₂ are O; NH₂, NH₃ ⁺, OH,or a hydrocarbon group having 1 to 3 carbon atoms that can besubstituted with a substituent, and the substituent includes a halogen,cyano group, hydroxyl group, phosphoric acid group, carboxyl group or asalt thereof).
 2. The method of manufacturing a cathode active materialfor a lithium secondary battery according to claim 1, wherein thelithium-sulfur-containing portion has a monoclinic crystal structure. 3.The method of manufacturing a cathode active material for a lithiumsecondary battery according to claim 1, wherein a sulfur content in thelithium-transition metal composite oxide particle measured through acarbon-sulfur (CS) analyzer is 2,000 to 7,000 ppm based on a totalweight of the lithium-transition metal composite oxide particle.
 4. Themethod of manufacturing a cathode active material for a lithiumsecondary battery according to claim 1, wherein an average sulfur signalvalue of the lithium-sulfur-containing portion measured through energydispersive spectroscopy (EDS) is greater than the average sulfur signalvalue in the primary particles measured through the EDS.
 5. The methodof manufacturing a cathode active material for a lithium secondarybattery according to claim 4, wherein the average sulfur signal value ofthe lithium-sulfur-containing portion measured through the EDS is 1.2 to3.8 times greater than the average sulfur signal value in the primaryparticles measured through the EDS.
 6. (canceled)
 7. The method ofmanufacturing a cathode active material for a lithium secondary batteryaccording to claim 1, wherein the hydrocarbon group included in R1 andR2 in Structural Formula 1 is substituted with or connected to at leastone selected from the group consisting of a carbon-carbon double bond,—O—, —S—, —CO—, —OCO—, —SO—, —CO—O—, —OCO—O—, —S—CO—, —S—CO—O—, —CO—NH—,—NH—CO—O—, —NR′—,

—S— and —SO2—, and R′ and R is a hydrogen atom or an alkyl group having1 to 3 carbon atoms.
 8. The method of manufacturing a cathode activematerial for a lithium secondary battery according to claim 5, whereinthe sulfonyl-based compound includes at least one of compounds ofFormulae 1 to 3 below:


9. The method of manufacturing a cathode active material for a lithiumsecondary battery according to claim 1, wherein the primary particleshave a hexagonal close-packed structure.
 10. The method of manufacturinga cathode active material for a lithium secondary battery according toclaim 1, wherein a content of lithium carbonate (Li2CO3) remaining onthe surface of the lithium-transition metal composite oxide particle is2,500 ppm or less based on the total weight of the lithium-transitionmetal composite oxide particle, and a content of lithium hydroxide(LiOH) remaining on the surface of the lithium-transition metalcomposite oxide particle is 2,000 ppm or less based on the total weightof the lithium-transition metal composite oxide particle.
 11. (canceled)12. The method of manufacturing a cathode active material for a lithiumsecondary battery according to claim 14, wherein the sulfonyl-basedcompound aqueous solution is formed by inputting the sulfonyl-basedcompound into a solvent, and a weight of the solvent is 2 to 20% byweight based on the total weight of the preliminary lithium-transitionmetal composite oxide particle.
 13. The method of manufacturing acathode active material for a lithium secondary battery according toclaim 12, wherein an amount of the sulfonyl-based compound input intothe solvent is 0.5 to 2.5% by weight based on the total weight of thepreliminary lithium-transition metal composite oxide particle.
 14. Themethod of manufacturing a cathode active material for a lithiumsecondary battery according to claim 1, wherein the heat treatment isperformed at 250 to 450° C. under an oxygen atmosphere.
 15. The methodof manufacturing a cathode active material for a lithium secondarybattery according to claim 1, wherein the preliminary lithium-transitionmetal composite oxide particle is mixed with the sulfonyl-based compoundaqueous solution without water washing treatment.
 16. A lithiumsecondary battery comprising: a cathode comprising a cathode activematerial layer including the cathode active material for a lithiumsecondary battery manufactured by the method of claim 1; and an anodedisposed to face the cathode.